Conduits or ducts which are designed to carry communication and other cables or the like are typically either buried in a network formed in the ground or carried overhead by utility poles. The aerial system is far less expensive to install and maintain, and thus, where utility poles are available, it is the preferred system.
Known aerial ducts merely consist of a tube, usually formed of some high tensile strength plastic material, such as high density polyethylene, which can be attached to the utility poles and which provides a single compartment within the tube for the passage of a communication cable or the like. Such tubes are normally provided at the work site on reels. However, because of their density and weight, it is only feasible to provide a limited length of the tubing on a reel. Moreover, because of its weight, the tube is expensive to ship and install. In particular, the high coefficient of friction between the cable and the tube precludes the installation of the cable by means of long pulls. Rather, only shorter lengths of cable can be pulled through the tube at one time.
Most significantly, the prior art aerial ducts are only designed to hold one cable. Thus, if after a cable is pulled through the system and is in use, if more communication capacity is needed, an additional cable cannot readily be pulled through the same tube. While such is possible, all of the problems discussed above are compounded in that it is very difficult and time consuming to attempt to pull a second cable into a tube that already has one cable randomly positioned therein. Thus, rather than merely adding a cable to an existing installed aerial system, the prior art generally dictates that a second system be installed when increased capacity is desired.